This proposal addresses some novel and unconventional means by which estrogen and the neurotrophin family of peptides may mediate differentiative effects within a major and understudied estrogen target region of the developing brain, the cerebral cortex. The studies investigate the mechanisms underlying the differentiative (neurite-promoting) actions of estrogen in the brain, a property I first described in organotypic cultures of the developing brain. My laboratory was also the first to demonstrate widespread co-expression of the estrogen and neurotrophin (trk) receptors in developing CNS neurons in vivo. Our working hypothesis is that co-localization of these receptor systems may lead to interdependency of their ligands and the sharing or convergence of their signal transduction pathways. The experiments study the organization of a putative macromolecular signaling complex whose activation may lead to convergence of estrogen and neurotrophin signaling. We will characterize the identity of the receptors involved and the functional consequences of estrogen and neurotrophin interdependency. Cross-coupling of converging estrogen and neurotrophin signaling may lead to similar nuclear end-points and regulation of the same genes. Organotypic explants (slices) of the developing cerebral cortex, derived from postnatal wild-type and ER-alpha knockout (ER-KO) mice and maintained as roller tube cultures, will serve as the primary model system. Neuronal (PC12; PC12-E2) and non-neuronal (MCF-7; CHO-K1) tumour cell lines will serve as methodological and correlative controls. Estrogen receptor expression and neuronal differentiation, including neurite growth, will serve as markers of some differentiative responses. Cultures will be analyzed correlatively by histological, molecular biological, biochemical, and immunological techniques. These studies have profound ramifications for the overall development of the CNS as well as for neurodegenerative diseases and neural repair. The results obtained will provide new information with great relevance for understanding the developmental actions and perhaps even the neuroprotective effects of estrogen in the brain. Understanding how estrogen influences differentiation and development in the CNS through its interactions with the neurotrophins may help explain recent findings that estrogen can exert effects on higher order cognitive processes and that estrogen or its deficiency may be risk factors for the development of the sexually dimorphic disorders of cognition (learning disabilities and attention deficit hyperactivity disorder), neurodevelopment disorders with cognitive deficits (schizophrenia) and neurodegenerative disorders (Alzheimer's disease).